Scientists at a conference in the US this week presented the results of a study where they found that eating walnuts appeared to help delay the onset of breast cancer in laboratory mice. However, at least one expert warned that studies in mice don’t necessarily translate to humans.
Dr Elaine Hardman, associate professor of medicine at Marshall University School of Medicine in Huntington, West Virginia, presented the findings of the study to the 100th Annual Meeting of the American Association for Cancer Research, which is taking place this week from April 18 to 22 at the Colorado Convention Center in Denver. Hardman has spent 15 years studying the role of diet in cancer.
While the study was performend on mice, Hardman and colleagues suggest that the essential omega-3 fatty acids, antioxidants and phytosterols in walnuts may confer similar benefits on humans and people should consider reaching for walnuts instead of less healthy foods when they fancy a snack.
Hardman said everyone knows that a healthy diet overall helps us avert all manner of chronic diseases:
“Walnuts are better than cookies, french fries or potato chips when you need a snack,” she added.
For the study, Hardman and colleagues fed mice a diet whose human equivalent would be 2 ounces of walnuts a day (2 ounces is about 57 grams or the weight of a an average egg). Another group of mice were fed a control diet more typical of the American diet.
Using standard tests they found that the walnut group had significantly lower incidence of breast cancer tumors, fewer glands with a tumor and the tumors were smaller.
Hardman explained that the lab mice typically have 100 per cent tumor incidence at five months, but for the walnut group this was delayed by at least three weeks.
Hardman said last year, when she and colleagues published similar findings in the peer reviewed journal Nutrition and Cancer, that scientists are starting to understand that diet probably accounts for one to two thirds of all cancers.
When they did a molecular analysis (according to the earlier reported study they compared the liver contents of both groups of mice) they found that increased intake of omega-3 fatty acids was probably the most likely contributor to the decline in tumor incidence, along with at least two other ingredients: antioxidants and phytosterols. All three compounds have been linked to slower cancer growth before.
“Making dietary changes to prevent cancer could do more to reduce the deaths from cancer than chemotherapy to treat cancer,” said Hardman, adding that medicine was increasingly looking to diet as a way to reduce cancer.
“With dietary interventions you see multiple mechanisms when working with the whole food,” Hardman told the conference this week.
“It is clear that walnuts contribute to a healthy diet that can reduce breast cancer.”
However, some experts remain sceptical, and one in particular warned against using results in mice to make recommendations about human diets.
Dr Peter G Shields, deputy director of the Lombardi Comprehensive Cancer Center in Washington, DC told WebMD that it was “outrageous” to suggest people should start eating more walnuts based on the findings of study on mice.
He said studies had shown that beta-carotene reduced lung cancer in animals, but when they did the pivotal study in humans, the smokers who consumed more beta-carotene developed more, not less, lung cancer.
Josephine Querido of Cancer Research UK said there was not enough evidence that eating walnuts prevents breast cancer in humans.
She told the BBC that a healthy balanced diet with plenty of fruit and vegetables played an important part in reducing the risk of many cancers.
For breast cancer the strongest risk factor was age, she said, explaining that 80 per cent of breast cancers are detected in women over 50 so attending screening is very important. Aside from that, “keeping a healthy body weight, limiting alcohol intake and taking regular exercise, can also help reduce breast cancer risk,” she added.
According to a press statement released last year, the American Institute for Cancer Research and the California Walnut Commission sponsored the research by Hardman and colleagues, but Marshall University said neither organization was involved in the interpretation or reporting of the findings.
Sources: American Association for Cancer Research, Marshall University, WebMD, BBC News.
Written by: Catharine Paddock, PhD